Epidemiology and lagged climatic drivers of pediatric viral lower respiratory tract infections in Tianjin, China (2023–2025)

Background Following the lifting of pandemic-era restrictions, China experienced a sharp resurgence in pediatric respiratory infections; however, post-pandemic epidemiological and climatic data on lower respiratory tract infections (LRTIs) from the temperate continental climate of northern China remain scarce. Methods In this retrospective, single-center surveillance study, we characterized the post-pandemic epidemiology of six respiratory viruses in children hospitalized with LRTI in Tianjin and assessed their pathogen-specific, lagged climatic associations. Children aged 0–18 years hospitalized between January 2023 and December 2025 were tested by targeted next-generation sequencing for human rhinovirus (HRV), adenovirus (ADV), respiratory syncytial virus (RSV), human bocavirus (HBoV), influenza virus (IFV), and human metapneumovirus (HMPV). Pathogen–climate associations were estimated using a quasi-Poisson model that adjusted for seasonality, secular trend, and lagged meteorological exposures. Results Among 2,597 virus-positive cases, the leading pathogens were HRV (30.7%), ADV (26.6%), and RSV (20.6%), followed by HBoV (12.1%), IFV (6.0%), and HMPV (4.0%). Age distributions differed by pathogen (p<0.05): RSV and HBoV predominated in infants and toddlers, HRV and HMPV in preschoolers, ADV in school-aged children, and IFV across the older preschool-to-school-age range; males predominated for all viruses except IFV. Five viruses peaked in December, whereas HBoV peaked uniquely in July. After adjustment for seasonality and secular trend, the unadjusted associations of IFV with humidity and temperature disappeared, indicating that they largely reflected shared seasonality. In contrast, RSV retained associations with temperature (RR 3.87, 95% CI 1.39–10.76) and wind speed (RR 5.46, 95% CI 2.39–12.47) at a 1-month lag, and HMPV with temperature (RR 13.3, 95% CI 1.64–108.3; imprecise given its low case count); HRV, ADV, and HBoV showed no independent climatic associations. Co-infections occurred in 116 cases (4.5%), most frequently HBoV+HRV (23.3%). Conclusion Post-pandemic pediatric viral LRTI in Tianjin shows distinctive pathogen-specific profiles in age, seasonality, and climatic sensitivity. The summer peak of HBoV and the seasonally independent climatic drivers of RSV and HMPV provide a preliminary basis that, if confirmed with higher-resolution data, could inform pathogen-tailored, climate-informed surveillance in northern Chinese megacities.